Olympic Stadium negotiations may drag on past end of October deadline

London's Olympic Stadium will host around 20 days of athletics a year but otherwise its future remains unclear. Photograph: Tom Jenkins for the Guardian

The future of the Olympic Stadium may not be resolved by the original deadline of the end of the month.

West Ham United are keen to become the main tenants of the stadium in time for the start of the 2014-15 season but are embroiled in tense negotiations with the London Legacy Development Corporation about modifications to be made to the stadium at a cost of up to £160m and who will pay for them.

The board of the LLDC, chaired by the London mayor, Boris Johnson, after the previous chairman, Daniel Moylan, was moved from the role after only four months, remains split on whether the solution should include West Ham or not.

The LLDC chief executive, Dennis Hone, told the Guardian that talks were entering the "end game" ahead of a crucial board meeting next week, but said there was no "knockout" bid and the arguments for and against football and the changes demanded by West Ham remained finely balanced. "If we can't come to a conclusion, in the scheme of things if it slips another month or two I'd rather get the right solution," Hone said.

"Yes, the stadium is tricky. But it's tricky because we want to get it right. I would hate to bung someone in there and see it fall apart in five years. If it takes a couple of extra months to get there, then so be it."

While football would attract large crowds on a regular basis, he said that aside from the stadium conversion there were also attendant costs in terms of the stewarding and transport considerations.

Hone said: "We've had discussions with all of the bidders. The difficulty is that we're balancing the adaptations we have to make to the stadium against the proposals that have come in and the benefits – financial and otherwise – that those proposals bring. If it was a knockout [verdict] it would be an easy decision, but it's not."

The other bids under consideration, which could be incorporated alongside West Ham rather than instead of them, are from Leyton Orient, a consortium wanting to hold Formula One racing in the Park – though that is unlikely – and a football business college.

It has already been decided that the £486m stadium will host about 20 days of athletics a year, including Diamond League meetings and the 2017 world championships, and will be available for community use. Newham council is contributing a £40m loan towards the project.

Once the main tenants have been decided, a stadium operator will be appointed to manage a programme of concerts and other sporting events.

Some at City Hall believe that, with the already iconic stadium having proved its worth as a concert and sporting venue during the Olympics, the LLDC should press on without football. But others, including Johnson, believe that West Ham still offer the most sustainable long-term solution while wanting to ensure that the deal is beneficial to taxpayers.

Whatever the solution, a full roof and permanent hospitality and toilet facilities need to be added to the stadium shell. But West Ham also want to bring temporary seating behind the goals, for which there are a number of options from stands that could be dropped into position for the football season to retractable seating. That also has implications for the roof, if it is to be extended to cover the temporary stands, which would need to be cantilevered over the existing structure.

Hone said it was important that any modifications were of high quality and would last for the long term without compromising the aesthetics and atmosphere of a stadium that had proved its mettle during the Games.

"My view is that if you're going to do adaptations, do quality adaptations that can last for 75 years and that we can all be proud of," he said. "But that's difficult to justify if the cost comes back on the public sector. Those are the imponderables we're working through at the moment."

It is understood that a decision on the stadium could be pushed back as far as December if no agreement is reached at this month's board meeting. The process, which had to be restarted after a previous attempt to award a long-term lease to West Ham collapsed under the weight of legal challenges from Spurs and Orient, has already had its deadline extended once to allow bidders to make modifications to their original bids.

The West Ham vice-chair, Karren Brady, last month underlined the club's credentials, promising the LLDC and taxpayers that it would not only bring "the most exciting and most watched football league in the world to Stratford" but "retain the Olympic legacy that Lord Coe feels so passionate about" through community work and local engagement.

West Ham are understood to be concerned about the impact of any further delay and remain keen to conclude a deal by the end of the month, convinced that their solution offers the only long term viable future for the stadium.

If the timetable slips much further, there are fears the club would struggle to make the move in time for the start of the 2014-15 season.